'I count him braver who overcomes his desires than him who conquers his enemies; for the hardest victory is over self.'

Aristotle joined Plato's academy at the age of 17 but soon came to disagree with his teacher. If Plato pointed to the sky then Aristotle pointed to the earth and turned Plato's theory of forms on its head.

He claimed that the world of perceived things is the real world and that there are no perfect forms in a realm beyond.

Knowledge, therefore, is not a grasping after forms but is built upon the careful grouping, naming, comparing and categorising of all the varied things as they appear in the world and that's exactly what Aristotle spend much of his life doing.

He appreciated the value of observation and wrote much about cause and effect in nature (especially his theory of four causes in the Physics). His writings covered biology, animal behaviour, the weather, planetary motions, stars and Gods as well as politics and ethics.

He helped develop the theory of the four elements - earth, fire, air and water - as the basic stuff matter and related them to the four humours - blood, choler, phlegm and bile.

He also espoused the doctrine of the golden mean (shared independently by Confucius) that the best path in life was the one between two extremes. It has come down to us as 'moderation in all things'.

More than Plato and Socrates Aristotle's brand of reason influenced the progress of Judaism, Islam and Christianity through thinkers such as Maimonides, Thomas Aquinas and Averroes.

Richard Sorabji, CBE is Emeritus Professor of Philosophy at King's College London, and Honorary Fellow of Wolfson College University of Oxford. He is a Fellow of the British Academy and an Honorary Member of the American Academy of Arts and Sciences. He is founder and director of the international 'Ancient Commentators on Aristotle' project devoted to the publication of translations of philosophical texts from the period 200-600 AD, texts that formed the necessary bridge between ancient philosophy and later thought both in Medieval Islam and in the Latin-speaking West. To date over 50 volumes have been completed. Richard Sorabji has written and contributed to many works of Aristotle including: Aristotle on Memory (2004); Necessity, Cause and Blame, Perspectives on Aristotle's Theory (1998) Aristotle transformed - the ancient commentators and their influence (1990); Aristotle and After (1990), Rejection of Aristotle (1987).